The role of domesticated animals in amplification and dissemination of La Crosse (LAC) virus has not been studied. Recent host preference studies have shown that white-tailed deer (Odocoileus virginianus) are frequent sources of blood meals for Aedes triseriatus, the principal mosquito vector of LAC virus. The susceptibility of deer to mosquito-delivered field-source LAC virus has not been determined. We will test dogs, cats, cattle, horses, pigs and deer to 1) determine if they can be infected by the bite of infected Ae. triseriatus mosquitoes, 2) develop viremias of sufficient magnitude and duration to infect susceptible Ae. triseriatus and 3) shed virus from throat secretions (dogs and cats) or milk (cows). We will test sera from domesticated animals from the LAC virus enzootic area for LAC virus neutralizing antibody to determine the relative frequency of infection. We will also place sentinel animals in an enzootic focus of LAC virus transmission to determine the rapidity with which they become infected. The capability of LAC virus to reassort in natural vertebrate hosts will be tested. Normothermic or hypothermic (torpor-induced) chipmunks (Tamias striatus) will be dually infected with ts LAC and snowshoe hare (SSH) viruses. Viremia will be tested for the presence of wild type viruses capable of growing at permissive (39.5 C) temperatures. The ratio of wild to ts virus will be quantified. We will conduct some pilot experiments to determine if LAC virus crosses the placenta of pregnant chipmunks and cottontail rabbits and persistently infects their young.